The invention relates generally to a method and apparatus for setting a time delay in a projectile fuze. More particularly, the invention relates to a method and apparatus for automatically setting a time delay in a digital type projectile fuze during the exit of the projectile from a gun barrel, wherein the time delay data is inductively transmitted from a transmitter secured to the barrel muzzle to a receiver located in the projectile.
The advent of terrain guidance missiles or low flying cruise type missiles has facilitated undetected penetration of outer defenses and greatly decreased the time between detection and target impact. Fast countermeasure response is also necessary under battle conditions such as an enemy helicopter rising from behind cover, sighting, firing, and descending behind cover before an air defense gun can respond properly and fire. Since these type threats can be considered "soft armored", the best countermeasure is often a high explosively fragmented projectile. The time response to these types of threats is so small that presetting a fuze prior to firing is impractical. Proximity type fuzes, which can be used for a fast response gun system, suffer in accuracy due to signal multi-path returns on low trajectory projectiles, especially when encountering targets over water.
U.S. Pat. No. 3,958,510, issued May 25, 1976 to Stutzle, describes a system for setting the fuze of a projectile as it leaves the muzzle of a gun by adjusting the magnitude of a magnetic field through which the projectile is passing. This system includes a control coil mounted on the muzzle of the gun barrel and a receiver coil mounted in the projectile. The amplitude of the induced current in the receiver coil which is generated during passage of the projectile through the control coil and which is used to set the fuze, is adjusted by adjusting the amplitude of a direct current supplied to the control coil. In this system, the amplitude of the induced voltage and receiver coil during passage through the control coil is dependent not only on the projectile velocity but also on the centering of the projectile within the control coil.
U.S. Pat. No. 4,142,442, issued Mar. 6, 1979 to Tuten, describes a system in which the time setting of the fuze of an artillery shell is digitally set after the shell has been fired but before it leaves the muzzle of the gun. The communications link for setting the fuze includes a transmitting coil mounted on the gun muzzle and a receiving coil mounted on the artillery shell. The transmitting coil is energized with a plurality of signals at discrete frequencies. The output from the receiving coil is detected to derive one binary digit representing each discrete frequency. All of the binary digits are simultaneously set into a binary counter in the fuze, so that the binary number represents the time delay setting for the fuze. This system requires a plurality of constant frequency oscillators in the transmitter, as well as a like plurality of filters tuned respectively to the frequencies of outputs of the oscillators.
U.S. Pat. No. 4,022,102, issued May 10, 1977 to Ettel, describes a much simpler system for adjusting a projectile fuze after firing a projectile out of a gun barrel, wherein information is transmitted inductively from a transmitter mounted in front of the gun barrel to a receiver located in the projectile. The passage of the projectile through a trigger coil mounted adjacent the barrel muzzle triggers the transmission of pertinent information and after such passage, information is computed and stored. Upon passage of the projectile through a transmitter coil disposed in front of and spaced from the trigger coil, the information is transmitted from the transmitter coil in the form of pulses to the receiver coil. The length of the transmitter coil and the frequency of the pulses are chosen so that all information can be transmitted during the time that the receiver coil is inductively coupled with the transmitter coil. These two spaced-apart coils mounted to the gun barrel are more difficult to shield against countermeasures signals and to protect against erosion by propellant gases than a single coil of very short length, such as described in my U.S. Pat. Nos. 4,228,397 and 4,486,710. Also, these two spaced-apart coils present a conspicuous target to enemy gun fire.